Threaded fasteners, including inherently torque-limited fasteners, are well-known in the art. High performance fasteners are quite expensive, and often are used in installations where excessive weight is objectionable not only because of the cost of the material, but because of added operational costs which may be proportional to weight. For example, each additional pound added to the weight of an aircraft adds considerably to its annual cost of operation.
Reduction in weight has been attained by the use of light-weight materials such as titanium, but weight savings from substitution of material are becoming increasingly difficult to make. It is an object to this invention to reduce the weight of a fastener by providing a structure whose thread length can be reduced, and thereby the length and weight of the pin can be reduced. Also, because collars for such installation usually have counterbores to contain the incomplete threads that are conventionally formed on the pin, the collars must be long enough for the counterbore and for the necessary length of its own thread. This requires the collar to be longer and weigh more. Having fewer incomplete threads requires a shorter counterbore, and therefore a shorter and lighter collar can be used.
High performance, inherently torque-limited fasteners and joints of the type disclosed herein are generically shown in George S. Wing Pat. No. 3.390,906, issued on Jul. 2, 1965. In addition, localized work hardening of pins is known, an example being shown in the U.S. patent application Ser. No. 108,959, filed Dec. 31, 1979, now U.S. Pat. No. 4,326,825, issued Apr. 27, 1982, by Josef F. Volkmann, Edwin E. Hatter and Michael M. Schuster, entitled "Balanced Pin For Shear Flow Joint, and Joint Including the Pin", which is owned by the same assignee as this instant patent application.
It is an object of this invention to provide an improved light-weight fastener, which optionally may include inherent torque-limiting features.